Method for preparing matrix protective coating

ABSTRACT

Disclosed a method for preparing a matrix protective coating, including a preprocessing step and a like transfer membrane coating preparation step. The like transfer membrane coating preparation step includes the following steps: mixing, drying and cooling YSZ powder and polytetrafluoroethylene powder to obtain a mixture, and then spraying the mixture onto the surface of a preprocessed matrix by an atmospheric plasma spraying method, wherein spraying parameters are set as follows: a moving speed of a spray gun is 440-460 mm/s; the current is 550-600 A, the voltage is 40-50 V, and the power is 24.8-30 kW; the compressed air is 0.6-0.7 MPa; the powder feeding carrier gas Ar is 3-6 L/min; a powder feeding rate is 25-28 g/min; and a spraying distance is 108-112 mm. The wear resistance of the coating of the present invention is significantly improved; the corrosion resistance is excellent; and the superhydrophobic property is excellent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from Chinese Patent Application No. 202011121503.6, filed on Oct. 20, 2020. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention belongs to the technical field of surface protection, and particularly relates to a method for preparing a matrix protective coating.

BACKGROUND OF THE PRESENT INVENTION

Organic polymers generally have low friction coefficient, but poor wear resistance and high wear rate, and are easy to fall off.

Researches show that surface protection is an effective way to improve the surface wear resistance of an organic polymer matrix. A patent document with a publication No. CN111701825A prepares cylindrical porous yttria (Y₂O₃) stabilized zirconia (YSZ) as a skeleton of a ceramic material by using suspension plasma spraying (SPS); the skeleton is filled with polyacrylonitrile (PAN)-modified PTFE self-lubricating polymer; and then a PAN-PTFE modified coating material is smeared on a YSZ coating, followed by vacuumizing under negative pressure and curing. The principle is as follows: YSZ suspension is directly subjected to plasma spraying as a spraying raw material to prepare the YSZ coating, so that the problem that nano powder is easy to grow up under a high temperature condition is solved; moreover, precursor micelles pass through plasma flame flow at high speed, the flying time is extremely short (less than 10⁻³ seconds), and nucleation nano crystals collide with the matrix before growing up and are deposited as the nano coating; secondly, polyacrylonitrile (PAN) can increase cohesion between a transfer membrane and a grinding surface, so that the transfer membrane can adhere completely and firmly to the grinding surface and is not easy to fall off, thereby reducing a cycling process from formation of the transfer membrane to falling of the transfer membrane to re-formation of the transfer membrane, and reducing abrasion loss; and furthermore, under the negative pressure, the PAN-PTFE modified coating material can be fully penetrated into the YSZ coating with conical cylindrical pores, thereby reducing the porosity of the YSZ coating, improving the compactness, reducing the friction coefficient and wear rate and improving the wear resistance. The coating prepared by the method has low friction coefficient and wear rate, can more efficiently play the corrosion resistance and hydrophobic property of a polytetrafluoroethylene material, and solves the problems of large abrasion loss and poor wear resistance. The wear rate is 80×10⁻⁶mm³·N⁻¹·m⁻¹, and the friction coefficient is 0.42. However, the coating prepared by the method cannot meet application needs.

SUMMARY OF THE PRESENT INVENTION

In view of this, a purpose of the present invention is to provide a method for preparing a matrix protective coating.

In order to realize the above purpose, the present invention adopts the following technical solution:

The method for preparing the matrix protective coating includes a preprocessing step and a like transfer membrane coating preparation step. The like transfer membrane coating preparation step includes the following steps:

mixing, drying and cooling YSZ powder and polytetrafluoroethylene powder to obtain a mixture, and then spraying the mixture onto the surface of a preprocessed matrix by an atmospheric plasma spraying method, wherein spraying parameters are set as follows: a moving speed of a spray gun is 440-460 mm/s; the current is 550-600 A, the voltage is 40-50 V, and the power is 24.8-30 kW; compressed air is 0.6-0.7 MPa; powder feeding carrier gas Ar is 3-6 L/min; a powder feeding rate is 25-28 g/min; and a spraying distance is 108-112 mm.

Further, the preprocessing step includes a sand blasting step. Further, sand blasting parameters are set as follows: 0.3-0.4 MPa air is taken as power; a spraying distance is 100-130 mm; an injection angle is 70° -90°; and multi-angular 60-150-mesh white fused alumina abrasive is injected to the surface of the matrix.

Further, a mixing ratio of YSZ powder to polytetrafluoroethylene powder is (92%-93%): (7%-8%), by mass percent.

Further, drying refers to drying for 3 h at 50-90° C.

Further, a thickness of the like transfer membrane coating is 20 μm-40 μm.

Further, the matrix is metal or ceramic material.

The present invention has the beneficial effects:

The wear resistance of the coating prepared by the method of the present invention is significantly improved. The average friction coefficient of the coating can be lowered to 0.1392. The wear rate can be lowered to 8.434×10⁻⁶ mm³·N⁻¹·m⁻¹.

The coating prepared by the method of the present invention has excellent corrosion resistance.

The coating prepared by the method of the present invention has excellent superhydrophobic property.

By using the method of the present invention to prepare the coating, during spraying, DC arc is generated between a cathode and an anode, which heats and ionizes the introduced working gas into high-temperature plasma and injects the plasma from a nozzle to form plasma flame. The central temperature of the plasma flame can reach 30000° k. The temperature at an outlet of the nozzle can reach 15000-20000° k. The flame flow velocity at the outlet of the nozzle can reach 1000-2000 m/s, but is attenuated rapidly. Mixed powder is delivered by a powder feeder into flame for melting, and after being accelerated by the flame flow to a velocity greater than 150 m/s, the mixed powder is injected onto the matrix material to form the coating. The high-temperature plasma can completely melte PTFE and partially or completely melt YSZ powder. Molten elements are solidified, which may impact the surface of the coating together with the non-molten YSZ powder, and a firm skeleton structure is formed to reinforce organic components, so that primary materials are prevented from falling off, and the coating with excellent cohesion may be formed on the surface of the matrix.

The present invention adopts outer flames to feed the powder, so that the PTFE components can be effectively prevented from being burned out, and the YSZ particles can arrive at a high-temperature zone under the effect of gravity to be molten completely. The YSZ powder that does not enter the high-temperature zone is kept at a particle state and has an impact effect on the deposited coating under the effect of the plasma flame flow, so that PTFE components in a liquid-phase zone are compacter and smoother, thereby achieving a like transfer membrane structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a preparation principle of a like transfer membrane coating.

FIG. 2 shows a test result of morphology and hydrophobic properties of surface interface and section structures of the coating.

FIG. 3 is a section view of the coating, including the coating;

FIG. 4 shows a test result of wear resistance, including sliding time; friction coefficient; wear rate; samples; and

FIG. 5 shows a test result of corrosion resistance, wherein on the horizontal axis, time is in Sec (second), and on the longitudinal axis, E refers to level, and the unit is volts.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Embodiments are provided to better explain the content of the present invention, and the content of the present invention is not limited to the provided embodiments. Non-essential improvements and adjustments made by those killed in the art for the implementation solutions according to the content of the present invention still fall within the protection scope of the present invention.

Embodiment 1

A method for preparing a matrix protective coating includes the following steps:

A, preprocessing, including:

a) Preparation of base materials: a 316 L stainless steel workpiece with a dimension of Φ25 mm*6 mm is taken and ground carefully with abrasive paper, and then burrs, welding slag, sharp corners, etc. on the surface are removed.

b) Sand blasting: 0.3-0.4 MPa dry and clean compressed air is used as power, under conditions that a spraying distance is 150 mm and an injection angle is 70°-90°, multi-angular granular 150-mesh white fused alumina abrasive is injected onto the surface of a matrix at a high speed, so that surface impurities can be cleaned thoroughly, and the surface is roughened to obtain a preprocessed surface layer.

B, Preparation of a wear-resistant coating:

a) Mixed powder composed of zirconia-yttrium oxide powder, i.e. YSZ powder (the content of yttrium oxide in the powder is 8 wt %) and polytetrafluoroethylene powder (PTFE powder) in a ratio of 92% (YSZ): 8% (PTFE) is mixed uniformly by a rolling ball mill for 2 h, and then the mixed powder is dried in a drying box for 3 h at 50° C. and then cooled to the room temperature.

B) The composite mixed powder cooled to the room temperature is sprayed uniformly by an F4 spray gun onto the surface of a preprocessed surface layer through a powder feeder by adopting an atmospheric plasma spraying technology. Spraying parameters are set as follows: the moving speed of the spray gun is 450 mm/s; the current is 600 A, the voltage is 50Y, and power is 30 kW; the compressed air is 0.6-0.7 MPa; powder feeding carrier gas Ar is 3 L/min; the powder feeding rate is 24 g/min; and the spraying distance is 110 mm. After the spraying, a finished product can be obtained, and the matrix does not need heat insulation and heating.

A preparation principle of a like transfer membrane coating is shown in FIG. 1.

It can be seen from FIG. 1 that YSZ powder and PTFE powder are quite different in melting points. In the present embodiment, the outer flame is used to feed the powder, so that the two materials can be ensured to play good performance. The temperature of the inner flame is far higher than the vaporization temperature of PTFE, so there is no PTFE component in the high-temperature zone. Although the outer flame is used to feed the powder, under the effect of the gravity, part of YSZ may present in the central high-temperature zone to reach a good molten state. When leaving the high-temperature zone and reaching a low-temperature zone far away from a muzzle, the powder may attain a relatively uniform state. The well-molten YSZ components and PTFE components may be deposited on the surface of the matrix. The YSZ forms a continuous skeleton structure to fix the PTFE components, thereby preventing primary materials from falling off. The non-molten YSZ has three states: 1, the non-molten YSZ is deposited together with the well-molten powder and fills the interior of the coating in a particle state; 2, the non-molten YSZ adheres to the surface of the coating; and 3, the non-molten YSZ is bounced off the surface of the coating due to insufficient impact force, and does not adhere to the coating, but plays a role in hammering and compacting the surface of the coating.

Performance Test

A Zeiss-ΣIGMAHD field emission electronic microscope is used to observe surface interface and sectional microstructures of the coating and observe whether water drops can form a spherical shape on the coating prepared in embodiment 1. Results are shown in FIG. 2.

It can be seen from FIG. 2 that the surface of the coating is relatively compact and has uniform bumps. However, the bums are relatively small in size, so the surface is relatively smooth.

The molten YSZ has higher energy. The PTFE can obtain a wide liquid-phase zone, so that the stress can be well released. Meanwhile, the stacked coating suffers a low impact energy of the non-molten particles continuously, so that the PTFE is hammed and compacted continuously in a solidifying process. Therefore, the coating has good compactness. The spraying angle is changed with the movement of the muzzle, thereby generating a shelter effect. Under the joint action of particle impact and shelter effect, the surface structure that is relatively compact and smooth and has uniform bumps is formed. This structure has some characteristics of a transfer membrane to a certain extent and is referred to as a like transfer membrane. This structure can be instantly transformed into the transfer membrane under the effect of an external force. The PTFE components make the coating surface have relatively low surface energy. The micro-nano bumps on the surface of the coating may trap air when the water drops are disposed to form a protective air pad, so that the coating surface may not be wet. Therefore, the superhydrophobic property is obtained (a water contact angle is 150.58°). This proves that the coating of the present invention has superhydrophobic property.

An MS-T3000 friction and wear test machine is used to test friction and wear properties. A Gcr15 stainless steel ball friction pair with a diameter of 6 mm is selected. Test parameters are set as follows: the rotation speed is 200 rap/min; the rotation diameter is 8 mm; the load is 5 N; and the friction test time is 90 min. Results are shown in FIG. 3.

It can be seen from FIG. 3 that a thickness of the coating is about 20 μm. The bump structure on the surface can be clearly seen, which provides an evidence for the superhydrophobic properties of the surface micro-nano structure of FIG. 1.

An ALPHASTEP D-100 step profiler is used to measure a section contour of a grinding crack. Results are shown in FIG. 4.

It can be seen from FIG. 4 that the average friction coefficient of the coating is 0.1392, and the wear rate is 8.434×10⁻⁶mm³·N⁻¹·m⁻¹. This proves that the coating prepared by the method of the present invention has excellent wear resistance. Under the load effect, the like transfer membrane structure is instantly transformed into the transfer membrane. The transfer membrane has the characteristics of surface smoothness, continuity and toughness. Therefore, the friction coefficient of the composite coating has a relatively low value. The filler YSZ forms a firm skeleton structure in the coating, so that not only are the PTFE components reinforced, but also the primary materials are prevented from falling off (the poor bonding property of the PTFE components severely limits the application range; and the skeleton structure effectively strains the PTFE components, so that the cohesion is effectively increased, and the PTFE components can be prevented from falling off). Moreover, the transfer membrane is reinforced and protected, so that secondary materials can be prevented from falling off (the transfer membrane formed by the PTFE components under the load effect is easy to fall off, and the YSZ filler can obviously enhance the quality of the transfer membrane and prevent under-surface damage and separate fragments). During grinding-in, abrasive dust of the composite coating is removed and compensated continuously; and after reaching a transition point, a matching end surface is fully filled with nano-scale fragments. These fragments exist continuously. The abrasive surface of the composite coating becomes smooth and compact, thereby guaranteeing the low friction coefficient and low wear rate of the coating.

An electrochemical corrosion open-circuit potential curve is tested by a CorrTestCS series electrochemical corrosion workstation designed and manufactured by Wuhan Contest Instruments Co., Ltd. Results are shown in FIG. 5.

It can be seen from FIG. 5 that the open-circuit potential of the coating already becomes a positive value greater than 0 after 8000 s and continues to keep rising. The open-circuit potential curve in FIG. 5 shows obvious fluctuation because hydrophobic property of the coating forms a layer of dense bubble barriers on the surface in a 3.5% NaCl solution environment and breaks the bubbles under the action of potential. The open-circuit potential is a positive value, so that the corrosion tendency of the coating is greatly reduced. This proves that the coating of the present invention has good corrosion resistance.

Furthermore, it should be understood that although this specification is described according to the embodiments, each embodiment does not include only one independent technical solution. The description of the specification is only for the sake of clarity. Those skilled in the art shall take the specification as a whole, and the technical solutions in each embodiment can be combined appropriately to form other embodiments that can be understood by those skilled in the art. 

1. A method for preparing a matrix protective coating, comprising a preprocessing step and a like transfer membrane coating preparation step, wherein the like transfer membrane coating preparation step comprises the following steps: mixing, drying and cooling yttria stabilized zirconia (YSZ) powder and polytetrafluoroethylene powder to obtain a mixture, and then spraying the mixture onto a surface of a preprocessed matrix by an atmospheric plasma spraying method; during spraying, direct current (DC) arc is generated between a cathode and an anode, which heats and ionizes an working gas into a plasma and ejects the plasma from a nozzle to form a plasma flame; the plasma flame includes an inner flame and an outer flame; a high-temperature zone having a temperature far higher than a vaporization temperature of the polytetrafluoroethylene powder is formed in the inner flame and a low-temperature zone having a temperature lower than the high-temperature zone is formed in the outer flame; the mixture is fed by the outer flame; the polytetrafluoroethylene powder is completely melt and the YSZ powder is partially melt molten polytetrafluoroethylene powder and molten YSZ powder are sprayed onto the matrix to form a deposited coating; a surface of the deposited coating is impacted by a non-molten YSZ powder; the non-molten YSZ forms a continuous skeleton structure to fix the molten polytetrafluoroethylene powder; wherein spraying parameters of the atmospheric plasma spraying are set as follows: a moving speed of a spray gun is 440-460 mm/s; a current is 550-600 A, a voltage is 40-50 V, and a power is 24.8-30 kW; a intensity of pressure of a compressed air is 0.6-0.7 MPa; the compressed air is used to carry and propel the mixture; powder feeding carrier gas Ar is 3-6 L/min; a powder feeding rate is 25-28 g/min; and a spraying distance is 108-112 mm.
 2. The method for preparing the matrix protective coating according to claim 1, wherein the preprocessing step comprises a sand blasting step.
 3. The method for preparing the matrix protective coating according to claim 2, wherein sand blasting parameters are set as follows: 0.3-0.4 MPa air is taken as power; a spraying distance is 100-130 mm; an injection angle is 70°-90°; the injection angle is an angle between the surface of the preprocessed matrix and a blasting stream; and 60-150-mesh white fused alumina abrasive is injected to the surface of the matrix.
 4. The method for preparing the matrix protective coating according to claim 1, wherein a mixing ratio of YSZ powder to polytetrafluoroethylene powder is (92%-93%): (7%-8%), by mass percent.
 5. The method for preparing the matrix protective coating according to claim 1, wherein drying refers to drying for 3 hat 50-90° C.
 6. The method for preparing the matrix protective coating according to claim 1, wherein a thickness of a like transfer membrane coating is 20 μm-40 μm.
 7. The method for preparing the matrix protective coating according to claim 1, wherein the matrix is metal or ceramic material. 